1. Field of the Invention
This invention relates generally to the field of blow molded plastic containers, and more particularly to a lightweight rectangular plastic container.
2. Description of the Related Technology
Many products that were previously packaged using glass containers are now being supplied in plastic containers, such as containers that are fabricated from polyesters such as polyethylene terephthalate (PET).
PET containers are typically manufactured using the stretch blow molding process. This involves the use of a preform that is injection molded into a shape that facilitates distribution of the plastic material within the preform into the desired final shape of the container. The preform is first heated and then is longitudinally stretched and subsequently inflated within a mold cavity so that it assumes the desired final shape of the container. As the preform is inflated, it takes on the shape of the mold cavity. The polymer solidifies upon contacting the cooler surface of the mold, and the finished hollow container is subsequently ejected from the mold.
Plastic containers must be designed to withstand different types of forces without excessive deformation. Adequate column or top load strength is required to prevent buckling or bulging of the container sidewall when the container is subjected to longitudinal compression, for example as a result of stacking of the containers during transportation. In addition, plastic containers must possess adequate circumferential or hoop strength to control deformation as a result of internal and external pressure differences.
In order to minimize material costs, it is desirable to make the sidewall of such containers as thin as possible. Such lightweighting, however, comes at the expense of container strength. Structural features such as grooves and ribs are often used to optimize the strength to weight characteristics of particular containers. For example, containers that have a substantially rectangular transverse cross-section commonly incorporate a narrowed circumferential waist portion, which enhances the hoop strength of the container and limits outward bulging of the container sidewall as a result of internal pressurization.
Another factor that often comes into play in the design of blow molded plastic containers is the suitability for a particular container design for receiving a label, such as a shrink-wrap label. Such labels must bridge structural features such as recessed grooves or the recessed waist of a rectangular container, which can create an unsightly appearance and potentially expose the label to damage when it is contacted by a consumer's fingernails or other object.
A need exists for a rectangular plastic container that possesses superior strength to weight characteristics in order to limit bulging of the container sidewall, while also minimizing deep surface dislocations that could interfere with the function of a label.